This section is intended to introduce various aspects of the art, which may be associated with one or more embodiments of the present disclosure. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present disclosure. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
Chemical usage is a fundamental aspect of current civilization. Facilities for the production, processing, transportation, and use of chemical species continue to be built in locations around the world. Thus, detection of chemical species is a continuing focus.
An example of chemical species detection is gaseous leak detection. As the efficiency of facilities becomes increasingly important, even minor losses of chemical species such as hydrocarbons can add to cost or create issues for regulatory agencies.
Hydrocarbons in facilities may be lost due to process limitations or process upsets leading to flaring or leaks. While some of these issues can be directly improved by design, leaks still provide a challenge, as they may occur on any number of different process equipment types. For example, leaks can originate from pipe flanges, valves, valve stems, sampling systems, and any number of other locations. As equipment is used and ages, leaks become increasing probable.
Conditions within a facility can increase the probability of leakage or exacerbate leaks when they do form. For example, facilities using high pressures or cryogenic temperatures can increase the probability of leaks. LNG plants are an example of such facility conditions. The number of LNG liquefaction plants around the world is growing rapidly and as these plants age, there is the increasing potential for hydrocarbon leaks to develop.
Early detection and repair of leaks can be useful in preventing any number of issues, such as increased costs and regulatory issues. Leaks may be detected by operators, for example, by visually observing the release, smelling the hydrocarbons, or hearing noise caused by the release. However, most hydrocarbon vapors are not visible to the naked eye. Further, there is often a high level of equipment congestion in plants, which may place a leak point behind another piece of equipment. In addition, hydrocarbons may have a minimal odor and, thus, may not be detected by smell. Detecting a small leak by sound is more improbable, as the very high level of ambient noise and safety equipment such as earplugs makes it unlikely that the leak will be heard.
Leak detection systems have been installed in many facilities. One such system may include combustible gas detectors that monitor the concentration or lower explosive limit (LEL) of hydrocarbon vapors at a particular location, providing a measurement of a hydrocarbon level at a point in an area. An array of point measurement systems may then be used to track a vapor release across the area. However, point detection systems may not detect small releases, such as from small leaks or new leaks, the amount of hydrocarbons released, and the like.
Another leak detection system that has been used utilizes a detection method that detects hydrocarbons in a line across a plant environment, for example, by directing a light source at one edge of an area towards a spectroscopic detector at another edge of the area. While such systems may be useful for monitoring compliance for regulatory issues, they do not necessarily identify a location of a release along the line. Further, they may not detect small releases at all for the same reasons as the point detectors, e.g., the hydrocarbons may be too dilute to detect or may be blown away from the detection line by the wind.
Another leak detection system has been described that can detect releases by imaging areas using cameras which can directly show an image of a hydrocarbon plume. One such system is described in Hackwell, J. A., et al., “LWIR/MWIR Hyperspectral Sensor for Airborne and Ground-based Remote Sensing,” Proceedings of the SPIE, Imaging Spectroscopy II, M. R. Descour, and J. M. Mooney, Eds., Vol. 2819, pp. 102-107 (1996). The system was named a spatially-enhanced broadband array spectrograph system (SEBASS). The SEBASS system was intended to explore the utility of hyperspectral infrared sensors for remotely identifying solids, liquids, and gases in a 2 to 14 micrometer spectral region often used to provide a chemical fingerprint. The SEBASS system allows the imaging and identification of chemical materials, such as hydrocarbon plumes, in an environment.
In a presentation entitled “The Third Generation LDAR (LDAR3) Lower Fugitive Emissions at a Lower Cost” (presented at the 2006 Environmental Conference of the National Petrochemical & Refiners Association, Sep. 18-19, 2006), Zeng, et al., discloses an autonomous system for leak detection that uses a camera to identify leaks in a particular area of a plant. Infrared (IR) video images from the camera are processed using software to minimize background and noise interference and the likely volatile organic compound (VOC) plumes are isolated using an algorithm. A plume index (PI) is calculated based on the number and intensity of pixels in the processed VOC plume image. If the PI is greater than an experimentally determined threshold value, an action can be triggered, such as an alarm or a video capture, for confirmation.
Another such system is described in WO2012/134796. The apparatus described therein includes multiple detectors configured to address complex interferences, such as moving equipment, people, vehicles, or steam, which can lead to false detections with a single detector system.
While the existing systems attempt to minimize background and noise interference, there is still a desire to obtain improved images for more accurate detection of chemical species.